Conveying systems are utilized in a variety of industrial settings. Manufacturing plants need such systems to quickly and efficiently transport articles between forming and assembling stations. Warehousing facilities transport articles between storage areas and/or to a loading dock with the use of conveying systems.
As production requirements have increased, it has become necessary to improve the speed of the transport systems within these facilities. This in turn has increased the need to control the conveyance of articles as they proceed along the desired travel path. Flow control is particularly important when the conveyed articles are subject to breakage. In this instance, it is critical to prevent a jarring impact when an upstream article catches up to a slower moving or stopped downstream article.
The speed and efficiency of movement along a conveyor system has evolved through the use of positive drive systems. The positive drive system typically involves the use of a prime mover, such as a motor, driving a timing belt that in turn drives the conveyor rollers to rotate at the desired angular velocity. Accordingly, the forward movement of articles traveling on the conveyors is predictably controlled.
It can be appreciated that the use of positive drive systems requires substantial capital investment as the drive components are incorporated within the conveyor system. Furthermore, the drive components require constant maintenance and increase the chance of failure and shutdown of the conveying system. The positive drive system also generates substantial energy costs during conveying operation.
Conveyor artisans have long recognized the advantage of relying upon gravity to effect the movement of articles from one place to another. Gravity conveyors obviously eliminate the need for positive drive mechanisms and the problems associated therewith. In spite of these advantages, gravity conveyors historically have been avoided because of the difficulty of transport control. Gravity conveyors have been particularly ill-suited for transport of articles of varying size and weight. In general, the terminal velocity of articles traveling on prior art gravity conveyors has not been predictable due to the above-described variables, as well as gap variation between articles.
In view of the basic simplicity and cost benefits of gravity conveyor systems, artisans have continued to attempt to find solutions to the problem of transport control associated therewith in order to avoid the use of positive drive systems. A common approach has been the integration of inertial devices within the gravity conveyor system to retard the forward movement of articles thereon. By varying the inertia of the conveyor rollers, a measure of control can be imposed on the system. An example of such an approach is disclosed in U.S. Pat. No. 2,607,459 to Ludwig et al., entitled "Retarding Roller for Conveyors". The Ludwig et al. roller contains a fluid that acts to slow rotation by shifting to seek a common level within the roller housing. This approach is illustrative of prior art attempts to promote control through passive means.
Various braking systems have also been devised for gravity conveyors. While the use of brakes to retard the rotation of rollers is not new, braking systems have previously been used principally to slow the forward movement of the article along the conveyor. Examples of different braking systems are disclosed in U.S. Pat. Nos. 5,048,660 to Kilper; 4,044,876 to Hammond; and 4,600,093 to Adams.
None of the above-cited references allow gravity conveyor systems to control the transport of articles with the desired precision and accuracy that is required by many modern facilities. There is thus a continuing need for a conveying system that can operate under gravity flow and provide the predictable transport capability that heretofore has only been available with conveyor systems using positive drive mechanisms. Such a gravity conveyor system would provide the desired control at a significantly lower cost and with greater simplicity than a system employing a positive drive mechanism.